How are neutron stars formed and what is inside them? What is the
engine powering short gamma-ray bursts? What is the astrophysical site
of production of heavy elements? Multimessenger observations of
compact binary coalescence and core-collapse supernovae might provide
us with the key to answer these and other important open questions in
theoretical astrophysics. However, multimessenger astronomy also poses
new challenges to the theorists who need to develop models for the
joint interpretation of all data channels. In this talk, I will
present recent theoretical results. I will review the landmark
multimessenger observation of merging neutron stars, and I will
discuss its interpretation and implication in the light of results
from first-principles simulations. Finally, I will discuss future
challenges and prospective for this nascent field.